1. Field of the Invention
The present invention relates generally to an electric arc furnace for melting metals, and more particularly to an electric arc furnace for melting metals which is capable of charging, melting, refining, and tapping on a continuous basis, and also to a method of melting cast iron by using the furnace.
2. Description of the Prior Art
Conventionally, the melting of metals by using an electric arc furnace is carried out by using raw materials supplied in one or more separate charges up to the capacity of the furnace and the molten or refined metal is tapped at one time. That is to say, in conventional electric furnaces, the charging and melting raw materials, and the tapping of molten metals are independent and intermittent operations, varying in volume in accordance with the size of the furnace. Conventional furnaces face the disadvantage that the adding of raw materials and tapping of refined metal require heavy labor. This is true, since if the tapping of large quantities of refined metal is done at one time, the temperature of the molten metal falls before it is treated or cast, causing differences in casting temperatures of the molten metal in individual castings, resulting in poor quality castings. Since molten metal which has been tapped in quantity at a given time must be handled quickly, large scale casting operations can be laborious, causing fatigue on the part of the workers involved.
Moreover, in the melting of metals, especially cast iron and nodular graphite cast iron, conventional melting processes are not efficient, particularly in removing harmful sulfur contained in the cast iron and in refining through deoxidation. The reason is that in such melting or refining, it is nearly impossible to prevent production of oxides of silicon (Si) in the molten metal. The presence of silicon oxides causes shrinkage cavities, resulting in the production of pin-holes or drossy scum, or other imperfections in the castings made of such molten metal. As these complications are nearly unavoidable in conventional melting methods, solutions have been sought in the metal melting process, a most difficult problem.
Another problem with the conventional electric are furnace is the inevitable production of dust and smoke in great volume during metal melting operations. This is a serious problem, especially because of air pollution. It cannot be prevented or reduced in conventional furnaces because of the difficulty in completely enclosing the top of the furnace due to the arrangement of electrodes in the form of a regular triangle on the top of the furnace. In addition, it is impossible to close up conventional furnaces and add dust collectors thereto due to their structure, which requires inclining the furnace, for ease in tapping molten metals.